In snow plowing applications, liability issues may require that a municipality or other jurisdiction be able to demonstrate that a particular stretch of roadway was plowed. While the location of a snow plowing vehicle can be demonstrated by recorded GPS/AVL data, the GPS/AVL data alone is not sufficient because it does not prove whether the snow plow blade was up or down. For example, an operator may have raised the snow plow blade(s) when passing through an intersection with an already-plowed street; it is necessary to prove that the operator lowered the snow plow blade(s) after passing through the intersection.
A number of technologies have been used to detect snow plow blade position. Most commonly, proximity switches and hydraulic pressure switches have been used but these approaches have high failure rates. The proximity switches are positioned externally and may be damaged, and the hydraulic pressure switches are prone to seize up during the summer months when not in use.
Snow plows typically use “air-over-hydraulic” control systems to effect a change in a snow plow blade position. Levers are used by the operator to allow the flow of regulated air to “air-piloted-valves” which in turn pilot respective hydraulic directional control valves operating a hydraulic cylinder to raise or lower the snow plow blade.
DiCAN Inc., having an address at 1100 Burloak Drive, Suite 300, Burlington, Ontario, Canada L7L 6B2, has introduced a system in which the flow of regulated air to each air-piloted valve passes a pneumatically activated switch, which generates an electrical signal when regulated air is supplied. Thus, the electrical signal indicates that a pneumatic control signal (“raise” or “lower”) has been applied to the hydraulic mechanism that controls the position of the plow blade, and this electrical signal can be transmitted to a GPS/AVL-equipped recording device so that the position of the plow blade at particular positions in a terrestrial coordinate frame (“geolocations”) can be logged. This detection arrangement obviates the high failure rate associated with proximity switches and hydraulic pressure switches.
Most of the conventional GPS/AVL-equipped recording devices are configured for conventional blade position sensors (e.g. proximity switches and hydraulic pressure switches) and are therefore configured to require a continuous electrical signal as to the position of the snow plow blade. However, the original DiCAN system only generates an electrical signal while the snow plow blade is being moved, and not while it is in a static position. This is because the flow of regulated air (which causes the electrical signal) is only applied to the air-piloted valve while the snow plow blade is actually being raised or lowered; the flow of regulated air (and therefore the electrical signal) ceases when the snow plow blade is in the desired position and the operator releases the lever. As a result, the original DiCAN system is not compatible with conventional GPS/AVL-equipped recording devices, and requires a specially programmed GPS/AVL-equipped recording device which can continue to record a plow blade position after the electrical signal has ceased. The specially programmed GPS/AVL-equipped recording device also applies a “time delay” factor, requiring a signal from the position monitoring system to persist for a predetermined period so as to exclude false positives (e.g. if the operator bumps the lever).
Because the specially programmed GPS/AVL-equipped recording device requires a constant, persistent signal of predetermined duration before recording a change in plow position (e.g. from “up” to “down” or vice versa), in certain circumstances an actual change in plow position may not be recorded. An operator may make several small movements of a snow plow blade, each of which is of a sufficiently short duration as to avoid triggering recordal of a change in plow position but which are cumulatively sufficient to change the plow position. For example, three or four individual half-second movements of the lever may be sufficient to raise the snow plow blade more than a foot or two off the ground (effectively meaning the plow blade is “up” rather than “down”). However, because each movement generates a signal that is shorter than the predetermined duration set in the specially programmed GPS/AVL-equipped recording device, the actual change in position of the snow plow blade is not recorded. Although such circumstances are relatively rare, when they do occur, the recorded snow plow blade position data will be inaccurate.
Accordingly, while the original DiCAN position monitoring system represents an improvement over conventional snow plow blade position sensors (e.g. proximity switches and hydraulic pressure switches), it suffers from the disadvantage of requiring a specially programmed GPS/AVL-equipped recording device and may fail to record the occasional large position change resulting from a series of smaller changes.